What is the simplest way to cause mass behaviour change amongst electricity consumers?

If you ask people in the industry, or in DECC, they say that people will only change their behaviour if they are financially motivated to do so via their electricity tariff. I'm not so sure.

Alex Laskey of Opower says that peer pressure is more important.

But first, people need some basic information on when to use electricity.

How about a traffic light system that tells people when it is most economic for the system as a whole - it would potentially save £50 billion in UK alone, if the alternative is a couple more large nuclear power stations.
At minimal cost, each home could have a light that changes colour when the supply situation changes. At its simplest, the light would be red between 3 and 8pm in winter, amber between 8am and 3pm in winter, and green pretty much all of the rest of the time.
Thus all members of each household would clearly know when it is environmentally and economically better to use or not use electricity.
Let me know what you think and tell your friends.